Swans: 'Do Our Butts Look Big?'

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A population of black-beaked swans known to winter in the United
Kingdom is dwindling, and researchers are looking for clues as to
why in an unusual spot: the birds' back ends.

That's because bird butts can signal lots about the animal's
diet, according to the Wildfowl and Wetlands Trust (WWT), a
conservation organization that is running the study. To find out
whether the birds are getting enough food to sustain them on
their
annual migration, WWT scientists and volunteers are checking
out the swans' behinds, a technique also known as "abdominal
profiling." A well-fed bird carries a little extra junk in the
trunk, between its legs and tail. In contrast, a scrawny,
underfed swan — the kind less likely to survive the journey north
— will lack a filled-out booty.

The Bewick's swan spends its winters in Europe and the U.K. and
flies to
Arctic Russia each spring. Even as other swan populations
have stayed stable, Bewick's swan flocks are dwindling. The
number of Bewick's swans wintering in Europe dropped 27 percent
between 1995 and 2005, from 29,000 to 21,000 individuals,
according to WWT.

One possible reason for the species' troubles is a lack of food
in their winter forage grounds in the U.K. – thus, the bird body
fat checkups, Julia Newth, a WWT researcher, said in a statement.
The data analysis isn't complete, Newth said, but early
observations suggest the birds are packing on plenty of fat for
their long journey. So if these results hold, and scrawny
derrieres aren't found, the researchers could rule out lack of
food at the wintering grounds.

"We need to do further work to see whether their body conditions
have changed over the years, and, if so, whether this is
connected with the decline in numbers," Newth said.

Various other factors could be hurting the swan population,
including habitat and weather changes at their breeding grounds
in Russia, as well as
poaching, collisions with power lines and lead poisoning,
according to WWT.

"Results from this year's observations will be compared with data
collected previously during the ‘80s, ‘90s and last winter,"
Newth said. "It will help rule out that the reduction in
overwintering swans is due to changes in habitat at U.K.
wintering sites — and give an indication of how the swans are
responding to environmental change."